[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: Re: [virtio-dev] [PATCH RFC 3/3] rng: leak detection support
On Thu, Aug 31, 2023 at 12:16:22PM +0200, Babis Chalios wrote: > Hi Michael, > > On 21/11/22 17:30, Michael S. Tsirkin wrote: > > Add virtqueues to support reporting entropy leaks (similar to virtio based vmgenid). > > > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com> > > --- > > virtio-rng.tex | 61 +++++++++++++++++++++++++++++++++++++++++++++++++- > > 1 file changed, 60 insertions(+), 1 deletion(-) > > > > diff --git a/virtio-rng.tex b/virtio-rng.tex > > index 1ec7164..4760dfa 100644 > > --- a/virtio-rng.tex > > +++ b/virtio-rng.tex > > @@ -9,10 +9,14 @@ \subsection{Device ID}\label{sec:Device Types / Entropy Device / Device ID} > > \subsection{Virtqueues}\label{sec:Device Types / Entropy Device / Virtqueues} > > \begin{description} > > \item[0] requestq > > +\item[1] leakq1 (only if VIRTIO_RNG_F_LEAK is offered) > > +\item[2] leakq2 (only if VIRTIO_RNG_F_LEAK is offered) > > \end{description} > > \subsection{Feature bits}\label{sec:Device Types / Entropy Device / Feature bits} > > - None currently defined > > +\begin{description} > > +\item[VIRTIO_RNG_F_LEAK (0)] Device can report and handle information leaks. > > +\end{description} > > \subsection{Device configuration layout}\label{sec:Device Types / Entropy Device / Device configuration layout} > > None currently defined. > > @@ -21,6 +25,7 @@ \subsection{Device Initialization}\label{sec:Device Types / Entropy Device / Dev > > \begin{enumerate} > > \item The \field{requestq} virtqueue is initialized > > +\item If VIRTIO_RNG_F_LEAK has been negotiated, \field{leakq1} and \field{leakq2} are initialized > > \end{enumerate} > > \subsection{Device Operation}\label{sec:Device Types / Entropy Device / Device Operation} > > @@ -41,3 +46,57 @@ \subsection{Device Operation}\label{sec:Device Types / Entropy Device / Device O > > The device MUST place one or more random bytes into the buffer > > made available to it through \field{requestq}, but it > > MAY use less than the entire buffer length. > > + > > +\subsubsection{Reporting Information Leaks}{Device Types / Entropy Device / Device Operation / Reporting Information Leaks} > > + > > +The device might, after the fact, detect that some of the entropy > > +it supplied to the driver has after the fact degraded in quality > > +or leaked to the outside world. One example is when the device > > +is part of the virtual machine undergoing a restore from snapshot > > +operation. Another example is when the information leaks from the > > +host system through a side-channel. > > + > > +The driver would typically react by causing regeneration of any > > +information that might have leaked and that has to be secret or > > +unique. It is understood that when an information leak has been > > +detected it is likely not limited to the entropy received through > > +the specific device. In particular, this is the case for > > +snapshoting It is thus suggested that the system fully > > +regenerate any unique/secret information in this scenario. > > + > > +If VIRTIO_RNG_F_LEAK has been negotiated the device can report > > +such leaks to the driver through a set of dedicated leak > > +queues: \field{leakq1} and \field{leakq2}. > > + > > +Buffers added to the leak queues can have one of two forms: > > +\begin{enumerate} > > +\item A write-only buffer. It will be completely filled by random data by the device. > > +\item A buffer consisting of read-only section followed by a > > +write-only section, both of identical size. The > > +device will copy data from the read-only section to the write-only > > +section. > > +\end{enumerate} > > + > > +The steps for operating the virtqueue are: > > + > > +\begin{enumerate} > > +\item At each time, only one of \field{leakq1}, \field{leakq2} is active > > + (has buffers added/used). > > +\item After initialization, \field{leakq1} is active. > > +\item Driver adds multiple buffers to the active leak queue. > > +\item The buffers are not used until an information leak is > > + detected, as long as that is the case driver can > > + add more buffers to the active queue. > > +\item Upon detecting an information leak, device starts > > + using buffers in the active leak queue. > > +\item Upon detecting that buffers have been used, driver > > + switches to another leak queue making it active > > + (e.g. from \field{leakq1} to \field{leakq2} or vice versa). > > + It then starts adding buffers to the new leak queue.\ > > I have been discussing with Alex and we think there's a potential race here, > between the time the driver > sees the used buffers in the active leak queue until the time it adds new > buffers to the next leak queue. > If a new entropy leak event arrives the VMM won't find any buffers in the > queue. I do not understand why this matters though. we know there was a leak, why does it matter whether there was one or two leaks? > In the last RFC implementing this in Linux we sent to LKML [1] we avoid the > issue by pre-populating both > queues, but that does not solve the problem if a third entropy leak event > arrives. The probability of this > happening is indeed small, but we thought of a potential solution to this. > > What if we modify the spec here to instruct the VMM to deny taking a > snapshot if there are not any buffers > in the active leak queue? If we did this, we could even simplify the spec to > just introduce a single entropy > leak queue, so we could avoid the complexity of switching between active > leak queues in the driver and > the device. WDYT? here's the problem: - driver adds batch 1 of buffers - leak - device starts using buffers from batch 1 - driver sees some buffers and starts adding batch 2 - device sees batch 2 and thinks this is part of batch 1 consumes them all > Cheers, > Babis > > [1] > https://lore.kernel.org/lkml/20230823090107.65749-3-bchalios@amazon.es/T/ > > --------------------------------------------------------------------- > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org >
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]